The effects of vitamin A deficiency on rhodopsin, opsin, and maintenance of retinal structure were examined in rats reared in low levels of cyclic light. The results show a rapid decline in the level of rhodopsin followed by a slower rate of opsin loss. Disruption of retinal structure more closely paralleled the loss of opsin. Both rod and cone photoreceptors are affected by vitamin A deficiency but rods are affected to a greater extent. Corneas of vitamin A deficient rats (low levels of retinoic acid) show several abnormalities before xerophthalmia is evident. The peripheral stroma becomes vascularized, and the keratocytes and histocytes show electron dense inclusion bodies. Corneal epithelial cells show an accumulation of electron lucent vacuoles and an increase in the extracellular space. The surface of the epithelium is highly irregular with many partially detached cells.